Method of straightening elongate inductively heated workpieces

ABSTRACT

A METHOD AND APPARATUS FOR INDUCTIVELY HEATING AND STRAIGHTENING AN ELONGATE WORKPIECE WHEREIN STOP MEANS. SUCH AS ROLLERS, ARE ADVANCED INTO CONTACT WITH THE HEATED WORKPIECE NOT EARLIER THAN IMMEDIATELY PRIOR TO CESSATION OF INDUCTIVE HEATING SO THAT THE ROTATING WORKPIECE IS STRAIGHTENED AS IT COLLS. IN ONE APPARATUS THE WORKPIECE HOLDING ELEMENT IS PIVOTABLE FROM A POSITION ADJACENT THE INDUCTOR TO A POSITION ADJACENT A QUENCHING COIL SO THAT THE WORKPIECE CAN BE QUENCHED IMMEDIATELY AFTER HEATING.

March 27, 1973 SEULEN ETAL 3,723,198

METHOD 0]" S'I'HALUH'IENLNG ELONGATE INDUCTlVlrJLY HEATED WORKPIECES vFiled NOV. 12, 1970 2 Sheets-Sheet 1 Fig.7

Fig.2 16 i Inventors March 27, 1973 SEULEN ETAL 3,723,198

METHOD OF STRAIGHTENING ELONGATE INDUCTIVELY HEATED WORKPIECES FiledNov. 12, 1970 2 Sheets-Sheet 2 Inventor 42 /7426? ,fl uzfiv Ear/mm EVA/Kggm M United States Patent 3,723,198 METHOD OF STRAIGHTENING ELONGATEINDUCTEVELY HEATED WORKPIECES Gerhard Seulen and Friedhelm Reinke,Remscheid, Germany, assignors t0 AEG-Elotherm G.m.b.H.,Remscheid-Hasten, Germany Filed Nov. 12, 1970, Ser. No. 88,548 Claimspriority, application Germany, Nov. 25, 1969, P 19 58 994.7 Int. Cl.C2ld 1/78 U.S. Cl. 148131 Claims ABSTRACT OF THE DISCLOSURE A methodand. apparatus for inductively heating and straightening an elongateworkpiece wherein stop means, such as rollers, are advanced into contactwith the heated workpiece not earlier than immediately prior tocessation of inductive heating so that the rotating workpiece isstraightened as it cools. In one apparatus the workpiece holding elementis pivotable from a position adjacent the inductor to a positionadjacent a quenching coil so that the workpiece can be quenchedimmediately after heating.

This invention relates to a method and apparatus for straighteningelongate workpieces which are held at each end and rotated while beinginductively heated by a linear inductor of the type whereinstraightening is accomplished by mechanical straightening means, such asstraightening rollers, straightening beams or sliding blocks.

One method and apparatus for inductively heating elongate and similarworkpieces as well as hardening their surfaces to major or minor depthsis described in Seulen et al., application Ser. No. 676,753, filed Oct.20, 1967, now Pat. No. 3,598,665, the disclosure of which is explicitlyincorporated herein by reference. In this method the electromagneticforces which are generated in the workpiece as it is inductively heated,urge the workpiece against the straightening means, usually idling ordriven straightening rolls, to thereby mechanically straighten the workat the same time as it is inductively heated. The method of thisprevious application has been found to be particularly successful forheating and straightening workpieces in which the temperature is desiredto be and is raised above the workpieces Curie point substantiallythroughout the cross-section. At this temperature all the stresses inthe workpiece are relieved and the straightening effect of the magneticfield in co-operation with the straightening rolls takes full effectwithout leaving residual stresses in the straightened work. I

However, if only the surface of the workpiece, while being inductivelyheated and straightened by this method, is heated to a depth less thansubstantially the entire cross-section, for example, between 10 and ofits diameter, for the purpose of subsequently hardening the surface byquenching, then considerable stresses remain in the core of theworkpiece. The magnetic forces and the reactive effect of thestraightening rolls generate residual stresses in the hardened partswhich reduce the fatigue strength and/or the torsional strength of thepart. Under many circumstances, this undesirable effect may even ariseif the entire interior of the workpiece is heated to temperatures abovethe Curie point.

The present invention relates to a method and apparatus overcoming thisdifiiculty so as particularly to permit satisfactory straight workpiecesto be obtained even when these are only locally heated for local surfacehardening. According to the invention of this application this isaccomplished by advancing the straightening devices into contact withthe rotating workpiece, not while 3,723,198 Patented Mar. 27, 1973 theinductive heating is taking place, but at the earliest, immediatelybefore the inductor is shut off. During the process of cooling, e.g.during the process of quenching, the workpieces are kept in contact withthe straightening devices, which are preferably straightening rolls,while the workpiece continues to rotate.

The optimum time for applying the straightening devices in anyparticular instance can be readily found by a few simple trials. In anyevent contact by the straightening devices should not be made at leastuntil immediately before the inductor is shut down, and may alternatelybe made at the same time or just after the inductor is shut down.Applying the straightening devices at this time ensures that thestresses in the workpiece can relieve themselves freely and that therolls or other straightening devices are not applied until this hasoccurred.

A particular advantage afforded by the method of this invention is thatit can be performed in equipment such as described in theabove-mentioned Seulen et a1. application containing straightening rollsthat can co-operate with the magnetic forces to straighten duringheating. The application of straightening rolls is preferablyautomatically controlled by reference to a time program and the rolls orother devices are advanced at the desired point in time, be itimmediately before, during or immediately after the shut-off of theinductor.

If it is intended to quench immediately after the cessation of heating,particularly when surface-hardening, then apparatus as hereinafterdescribed may be used. The apparatus consists of a tilting workholderunit, equipped with workholding means for mounting the elongatedworkpieces and with straightening rolls, for conveying the workpiecefrom a heating station facing the stationary inductor to a quenchingstation facing a quenching spray in a simple tilting motion that can berapidly performed.

Embodiments of the invention are hereinafter described and illustratedin the accompanying drawings, of which:

FIG. 1 shows a schematic representation of an apparatus for performingthe method of the present invention,

FIG. 2 shows a side elevation view of the workholding unit,

FIG. 3 shows an alternative form of construction of the workholdingunit, and

FIG. 4 shows a side view of a tilting unit according to the invention.

Referring to FIG. 1, a conventional current inducing apparatus having alinear inductor 2, and a return conductor 4 is provided adjacentworkpiece 1 for inductively heating the workpiece. Inductor 2 ispreferably fitted with laminated plates or a pressed soft iron magneticcore to provide a magnetic circuit generally indicated at 3. Thetransient direction of flow of the current through the inductor 2 andreturn conductor 4 and the current induced in the workpiece 1 which ispreferably rotating in the direction of the arrow 8 are indicated by across and a dot in a circle, the cross designating a current into theplane of the drawing. It is, of course, understood that the currentdirections and direction of rotation can be reversed if desired.

If the workpiece 1 consists of a non-magnetic material or a material ata temperature above the Curie point, then the work will experience athrust acting in the direction indicated by the arrow 7. As discussed inthe above-mentioned Seulen et a1. application this thrust can beutilized for straightening the workpiece by providing stops, such asstraightening rolls 5 and 6 against which the rotating workpiece ismagnetically urged. However, according to the invention of thisapplication, particularly if only the workpiece surface is to be heatedfor subsequent hardening, the rolls are not advanced during heating sothat straightening takes place not during heating but rather themagnetic forces are allowed freely to take effect during inductiveheating while the straightening rolls are in a retracted position. Thestraightening rolls and 6 which are movable as indicated at arrows 9 arenot advanced into contact with the rotating workpiece in the directionof the arrow 10 until, at the earliest, immediately before inductor 2 isshut'otf.

In practice the best time for infeeding the rolls 10' in dependence uponthe operation of the inductor is easily determinable by trial for aparticular operation. As mentioned above, that time may be immediatelybefore, during or immediately after the shut down of the inductor.

For performing the method according to the invention in the describedarrangement in a continuous production line it is preferred to make useof apparatus which is also conventional, a side view of one of which isshown in FIG. 2. Immersed in a tank 11 filled with a quench 12 is anindexable workholder unit 13 which permits enlongated workpieces 14 tobe horizontally mounted. Unit-13 is rotatable about its longitudinalaxis, and distributed about its periphery there are provided at leastthree or more individual workholders. Each workholder supports theworkpieces 14 on rolls 15 which participate in indexing motions of forexample 12, 90, 60 or 45, depending upon the number of workholdersdistributed around the periphery.

An inductor 16, such as the one shown in FIG. 1, is provided adjacentunit 13 for heating workpieces preparatory to straightening andhardening as described above. At regular or irregular intervalsdetermined, for instance, by an adjustable time delay relay, orfunctionally depending upon the surface temperature of the work,workholder unit 13 is indexed 90 in the direction indicated by arrow 17.The workpiece 14 including the straightening rolls 15 are thus immersedin quench 12 after inductive heating and straightened while beingquenched. If desired an additional spray 18 may be provided foraccelerating the quenching effect. The workpiece continues to be rotatedin the direction of the arrow 19 while it is being quenched, butrotation in the opposite direction would be equally acceptable. Theindexing intervals of the workholder unit are determined by the timeneeded for heating, since at least three times the heating time isavailable for quenching if the workholding unit is fitted with fourseparate workholders. However, if the workholder unit is provided withmore workholding positions, then the quenching time may be furtherprolonged in relation to the heating-up time. It may be desirable toprovide a supplementary quenching spray 18a in direct proximity with theinductor 16 to permit quenching to start with a minimum of delay afterheating has been completed, and without having to wait for theworkholding unit to complete its indexing motion. The rolls 15 are notadvanced into contact with the workpiece during the performance of theprocess, as shown in the drawing, until the cooling and quenchingprocess begins or just before.

It will be apparent that the same apparatus could also be used forhardening and straightening during heating as set forth in theabove-mentioned Seulen et al. application. Accordingly, a singleapparatus can be used for both methods.

Instead of horizontally mounting the workpieces as in FIG. 2, theworkpieces may be vertically mounted, as shown in FIG. 3. In thisembodiment the workpieces 14 are each heated in turn by an inductor 20at a first station of the workholding unit. After heating each workpieceis first indexed to the quenching spray 22 while continuing to rotate inthe arrowed direction, and then to position adjacent a second sprayer23. When the workpieces are being treated according to the novel methodof this application, the rolls 15 are not, of course, applied to theworkpiece 14 until the inductor 20 has been shut off or just before oruntil cooling or quenching begins.

FIG. 4 is a side elevational view of apparatus which may be moreparticularly used when quenching is to begin as quickly as possibleafter heating has been completed, and principally when the workpiece isto be surfacehardened. The apparatus illustrated is a tiltingworkholding unit 24 which is tiltable in bearings 25. The shaft thatworks in these bearings 25 may be vertical or horizontal, the tiltingunit either swivelling in the horizontal or tilting in the vertical. Thetilting unit carries two workholders for the ends of a workpiece 26 thatis to be treated. Straightening rolls 27 can be forced into contact withthe workpiece in the direction indicated by the arrows 28. In theheating position the workpiece 26 is held facing inductor 29.. When theheating process is concluded the tilting unit is tilted in the directionof the arrow 30 and thus carries the workpiece 26 without delay into thequenching position facing the quenching sprayer 31. The straighteningrolls 27 in this apparatus are likewise advanced in the direction of thearrows 28 into contact with the workpiece 26 at the instant the inductor29 is shut off.

"Instead of tilting the workpiece substantially in the horizontal, thetilting unit may also be so disposed that the workpiece is lowered froman upper position downwards, substantially vertically. This latterarrangement may particularly be used when quenching of the workpiece isto take place in an agitated liquid quench and the surface of the quenchis at a level high enough to permit the tilting unit to immerse theworkpiece bodily in the quench.

For loading and unloading the tilting workholding unit it may be movedinto a zero position 32 where a hardened and straightened workpiece canbe removed and an untreated workpiece substituted. During this processthe straightened rolls 27 are withdrawn.

Many changes and modifications of the above described embodiments of theinvention can, of course, be made without departing from the scope ofthe invention and accordingly that scope is intended to be limited onlyby the scope of the appended claims.

What is claimed is:

1. A method of heating and straightening an elongated metal workpiececomprising the steps of:

inductively heating said workpiece,

rotating said workpiece, and

advancing stop means into contact with one side of said rotatingworkpiece not earlier than immediately before cessation of said heatingand maintaining contact-during coding so that said workpiece isstraightened while it cools.

2. A method as in claim 1 wherein said workpiece is rotated during saidheating.

3. A method as in claim 1 further including the step of quenching saidworkpiece after said heating.

4. A method as in claim 3 wherein said workpiece is held in an indexingunit having a plurality of workholding means each adapted to hold aworkpiece, at least a single inductive heating station and at least asingle quenching station and further including the step of shifting saidworkpiece, after heating, from said heating to said quenching station.

5. A method as in claim 1 wherein said stop means are rollers andfurther including the step of rotating said rollers.

6. A method as in claim 1 wherein said stop means are advanced intocontact with said workpiece immediately before cessation of saidinductive heating.

7. A method as in claim 1 wherein said stop means are advanced intocontact with said workpiece at roughly the same time as cessation ofsaid inductive heating.

8. A method as in claim 1 wherein said stop means are advanced intocontact with said workpiece immediately after the cessation of saidinductive heating.

9. A method of straightening elongate workpieces held at each end whilebeing rotated about their longitudinal axis and heated by a linearinductor, using a mechanical References Ci d straightening device;wherein the said straightening device UNITED STATES PATENTS is advancedinto contact with one side of the rotating workpiece at a point in time,at the earliest, immediately 3,598,665 8/1971 Semen et before theinductor is shut off, and subsequently remains 5 3,562,030 2/1971 Seuknet 148-131 in contact with the rotating workpiece, and the work-3,255,053 6/1966 Bard 148-131 516?; cooled while 1n contact with thesaid straightening RICHARD 0. DE Primary Examiner 10. A method accordingto claim 9 wherein the work- U S C1 X R piece is quenched while incontact with the said straight- 10 ening device. 148-143, 150, 154;21910.41

